1. Field of the Invention
The present invention relates to a side bearing assembly for a vehicle. Specifically, the invention relates to a side bearing assembly including an insulator for storing energy when the insulator is subjected to compressive forces.
2. Description of the Related Art
Side bearing assemblies for railway vehicles are known in the art. Generally, railway vehicles include a truck, i.e., a wheel assembly, and a car body disposed on the truck. For example, the car body could be a tanker. The truck includes a plurality of bolsters extending transversely across the truck. Each bolster of the truck includes a center bowl and the car body includes a body center plate corresponding to each center bowl. One of a pair of side bearing assemblies is attached to the bolster on either side of the center bowl. Each center bowl pivotally receives the corresponding body center plate such that the car body is laterally pivotal relative to the truck in the center bowl. The car body is supported by the center bowl and each of the pair of side bearing assemblies. The side bearing assemblies are often referred to as constant contact side bearing assemblies because each of the pair of side bearing assemblies remains in constant contact with the car body of the railway vehicle. If contact between the car body and the side bearing is interrupted, the car body may slide relative to the bolster, which increases the potential for derailment.
The truck includes wheels that ride on tracks. Due to the shape of the wheels and the shape of the tracks, when the railway vehicle moves along a straight section of the track, the wheels are constantly hunting, i.e. searching, for a centered position on the track. Due to the hunting, the truck of the railway vehicle will oscillate relative to the track. As the truck oscillates relative to the track, the car body laterally pivots on the center bowl. As the car body laterally pivots, the car body makes a compressive movement to compress one of the side bearing assemblies of the pair of side bearing assemblies while simultaneously making a decompressive movement to decompress the other side bearing assembly of the pair of side bearing assemblies. The oscillation of the truck relative to the track increases as the speed of the railway vehicle increases, which increases the lateral pivoting of the car body relative to the truck. At high speeds, forces generated by the oscillation of the truck and forces generated by the car body laterally pivoting relative to the truck can cause the wheels to climb off the track resulting in derailment of the railway vehicle.
The side bearing assemblies dampen the lateral pivoting of the car body relative to the truck. The lateral pivoting of the car body repeatedly loads compressive forces on the cap and unloads the compressive forces from the cap. When the car body loads compressive forces on the cap, the insulator is compressed between the cap and the cage. When the car body unloads force from the cap, the insulator decompresses and delivers the energy back to the cap to urge the cap upwardly and to keep the cap in constant contact with the car body. In other words, the insulator is constantly urging the cap upwardly to maintain contact between the cap and the car body. Because an increase in the speed of the railway vehicle results in an increase in pivoting of the car body relative to the truck, the increase in speed of the railway vehicle increases the lateral pivoting of the car body. Therefore, the speed of the railway vehicle is limited by the ability of the side bearing assembly to dampen the pivoting of the car body relative to the bolster.
For example, a side bearing assembly is disclosed in U.S. Pat. No. 3,712,691 to Cope (the '691 patent). Specifically, the '691 patent discloses the side bearing assembly including a cage for attachment to the bolster, a cap disposed over the cage, and an insulator disposed between the cap and the cage. The cap contacts and supports a portion of the car body and is moveable relative to the cage. The insulator of the '691 patent is made from a rubbery material.
On occasion railway vehicles are operated in relatively cold temperatures. When the insulator is subjected to relatively cold temperatures, the flexibility of the insulator is decreased. In other words, in relatively cold temperatures the insulators are significantly less compressible. Accordingly, cold temperatures decrease the ability of the insulator, such as the insulator in the '691 patent, to dampen the lateral pivoting of the car body relative to the truck. Because the speed of the railway vehicle is limited by the dampening capability of the side bearing assembly, when the dampening capability is decreased at relatively cold temperatures, the speed of the railway vehicle must also be decreased. It is desirable to manufacture a side bearing assembly including an insulator that maintains flexibility at relatively cold temperatures.
In addition, the current insulators have a relatively small compression travel, i.e. the difference between the height of the uncompressed insulator and the height of the compressed insulator. When subject to compressive movement of the car body, the insulator is compressed and the height of the insulator is decreased. When subject to decompressive movement of the car body, the insulator decompresses and retains its height. When subject to decompressive movement, the insulator must decompress and exert force on the cap such that the cap remains in constant contact with the car body. If the compression travel is insufficient such that the insulator does not exert sufficient force on the cap, then the contact between the cap and the car body is interrupted, which can lead to movement of the car body relative to the bolster and increase the potential of derailment. Because increased speed of the railway vehicle increases the pivoting of the car body relative to the bolster, the speed of the railway vehicle is limited by the compression travel of the insulator. Current insulators are too rigid and too incompressible such that the compression travel of the insulators is insufficient to maintain constant contact at higher speeds. It is desirable to manufacture a side bearing assembly including an insulator with improved compression travel such that the insulator exhibits more compression travel and absorbs larger forces produced by increased pivoting of the car body relative to the truck at high speeds.